Piezo-Actuated Distributed Bragg Reflector–Based Tunable Fabry–Pérot Filter for Visible Light Hyperspectral Imaging

A tunable air-gap Fabry–Pérot filter consisting of distributed Bragg reflectors as cavity mirrors was developed to operate in the visible wavelength range. The wavelength tunability of the filter was achieved based on the piezo actuation mechanism. Four in-plane identical piezo actuators were employed to simultaneously achieve both wavelength tunability and cavity air-gap parallelism in the filter. Two pairs of piezo actuators positioned at crossed locations enabled independent control of cavity air-gap dimensions along orthogonal directions in the cavity plane. Optical transmission measurements were performed at different spatial positions on the cavity region to estimate the cavity air-gap dimensions. The initial maximum spectral separation among different spatial positions owing to the initial non-parallelism of the cavity air gap was estimated to be ∼28 nm. After achieving cavity air-gap parallelism via piezo actuation, the final maximum spectral separation was reduced to ∼3 nm. The proposed device configuration significantly improved the cavity air-gap parallelism by minimizing the maximum variation of the cavity air-gap dimension from an initial value of 535 nm to a final value of 18 nm, resulting in an improvement by a factor of ∼30. This device prototype can enable high-resolution and high-throughput spectral transmission with improved spatial uniformity across a large cavity area, showing great promise for advancing hyperspectral imaging systems.